Threatening by daughter in law

My brother married 1 and half year back. he had known the girl since november 2014. my brother and his wife took another house and stayed separately right after marriage (not with in-laws). only them in the house. my family only demanded that they should be loved and respected, nothing else. (just for info- no dowry was taken). my brother kept giving her chances and time. she disrespected him personally, infront of his friends, his career, did not respect his festivals, nothing. And 3 months back, she and her family tried to prove my brother's head is not working and mental. and 3 big doctors has said nothing is wrong, little depression. when she could not prove all this and kept on, my brother decided to give her divorce. she agreed. but then denied. and now she is threatening my brother (who is abroad for his job) that, she will file harassment case against his family, which is not all true. she keeps on threatening. she is a well educated, has a good paying job abroad for which she will shift soon. her family is well educated too. my brother wants to divorce her, but she is not ready. He stayed in mumbai but have shifted abroad. and his parents stays in navi mumbai.